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United States Patent |
6,091,016
|
Kester
|
July 18, 2000
|
Solar panel assembly
Abstract
Solar panel assembly comprising a number of rectangular panels each
carrying solar cells on one of the two main surfaces, said panels being
interconnected by mutually parallel hinges such that the assembly from a
first state, in which the panels are folded zigzag wise into a package,
can be brought into a second state in which the package is unfolded and
the panels are situated alongside each other in one plane. In the unfolded
state each panel is curved in a direction parallel to the panel edges to
which said hinges are attached.
Inventors:
|
Kester; Gerardus Joseph Adrianus Nicolaas (Vinkeveen, NL)
|
Assignee:
|
Fokker Space B. V. (Leiden, NL)
|
Appl. No.:
|
026430 |
Filed:
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February 19, 1998 |
Foreign Application Priority Data
Current U.S. Class: |
136/245; 136/292 |
Intern'l Class: |
H01L 025/00 |
Field of Search: |
136/245,292
|
References Cited
U.S. Patent Documents
3326497 | Jun., 1967 | Michelson | 136/245.
|
5833176 | Nov., 1998 | Rubin et al. | 136/245.
|
Primary Examiner: Chapman; Mark
Attorney, Agent or Firm: Young & Thompson
Claims
It is claimed:
1. In a solar panel assembly comprising a number of rectangular panels each
carrying solar cells on one of the two main surfaces, said panels being
interconnected by hinges such that the assembly from a first state, in
which the panels are folded zigzag wise into a package, can be brought
into a second state in which the package is unfolded and the panels are
situated alongside each other in one plane; the improvement wherein in the
unfolded state each panel is curved in a direction parallel to the panel
edges to which said hinges are attached, whereby the panel edges to which
said hinges are attached are non-rectilinear.
2. Solar panel assembly according to claim 1, wherein each panel shows only
one curve, defining a concave or convex shape of the assembly.
3. Solar panel assembly according to claim 1, wherein each panel shows two
or more adjacent curves.
4. Solar panel assembly according to claim 3, wherein the adjacent curves
define a number of adjacent concave or convex surface sections of the
assembly.
5. Solar panel assembly according to claim 3, wherein the adjacent curves
define alternating convex and concave surface sections of the assembly.
6. Solar panel according to claim 1, wherein each curve is obtained as a
fluent bend of the panel.
7. Solar panel assembly according to claim 1, wherein each curve is
obtained by a discrete number of bends with flat panel sections in
between.
8. Solar panel assembly according to claim 1, wherein the panels are made
of a resilient preformed material such that in the folded state of the
assembly each panel is stretched to a flat shape, whereas after unfolding
each panel resumes its preformed curved shape.
9. Solar panel assembly according to claim 1, wherein the panels are formed
as flat panels and the assembly comprises mechanical means which after
unfolding of the assembly can be activated to obtain the desired
curvatures in the panels.
10. Solar panel assembly according to claim 9, wherein the mechanical means
consist of tensioning means connected at least to both side edges not
connected to the hinges of a panel being able to draw these two side edges
towards each other over a predetermined distance.
11. Solar panel assembly according to claim 10, wherein the tensioning
means comprise plural crossing tensioning members extending in opposite
diagonal directions across at least one said panel.
12. Solar panel assembly according to claim 9, wherein the tensioning means
comprise wires and fasteners for shortening the length of said wires.
13. Solar panel assembly according to claim 9, wherein the tensioning means
comprise a number of bow shaped bridging elements, initially lying flat on
the surface of a panel, connected near the side edges to the respective
panel and connected with its bow shaped side at at least one further place
to the surface of said panel, such that after bringing this bridging
element into a state wherein it projects from the surface the panel is
forced to assume its desired curved shape.
14. Solar panel assembly according to claim 1, wherein the hinges are
embodied such that the transformation from a flat panel into a curved
panel is not impeded.
15. Solar panel assembly according to claim 14, wherein the hinges are
embodied as elongated hinges extending along the major part of the edges
to be interconnected and having enough flexibility to enable curving of
the respective panels.
16. Solar panel assembly according to claim 14, wherein the hinges are
embodied as relatively small hinges of arbitrary construction, a number of
which are, in a bow, attached to the edges to be interconnected.
Description
The invention relates to a solar panel assembly comprising a number of
rectangular panels each carrying solar cells on one of the two main
surfaces, said panels being interconnected by mutually parallel hinges
such that the assembly from a first state, in which the panels are folded
zigzag wise into a package, can be brought into a second state in which
the package is unfolded and the panels are situated alongside each other
in one plane.
Such solar panel assemblies are generally known. Typical examples are
described as state of the art in U.S. Pat. No. 5,31,905, U.S. Pat. No.
5,520,747 and EP-0,120,662.
Before transport the panels of such a solar panel assembly are folded
zigzag-wise into a package of which the length and width correspond
approximately with the length and width of one separate panel and of which
the thickness corresponds approximately with the thickness of one panel
multiplied by the number of panels. In this state the assembly is
transported from the earth into an orbit in space. In general the
transporting vehicle (rocket, space shuttle, etc.) is able to transport
payloads of rather restricted dimensions and restricted weight. Therefore,
it is required in general that solar panel assemblies have a low weight
and dimensions which should be within certain limits. To maintain a low
weight one could use stiffness-efficient constructions having a sufficient
strength, such as constructions comprising a lot of air and still having a
sufficient stiffness and strongness, such as for instance honeycomb
sandwich panels.
In general the only way to reduce the dimensions of a solar panel assembly
is to reduce the thickness of the actual panels. In case honeycomb
sandwich constructions are used the only reduction possibility is to
reduce the dimensions of the core. The surface, i.e. the length and width
of each panel, will be selected as large as possible to obtain a large
useful area for locating solar cells.
A too far reduction of the weight may lead to a construction having a too
small stiffness, both in stowed configuration and in the fully deployed
configuration. During operation that may lead to harmful bending and
torsion movements or oscillating movements of the individual panels or of
the assembly as a whole in its extended second state. Such movements may
occur for instance in the situation in which the position of the assembly
in relation to the carrying satellite has to be corrected.
The object of the invention is now to indicate how the constructive
stiffness of the extended solar panel assembly can be improved still
allowing the use of relative thin constructions and lightweight materials
for the panels.
In agreement with said object the invention now provides an assembly as
described in the first paragraph, characterized in that in the unfolded
state each panel is curved in a direction parallel to the panel edges to
which said hinges are attached.
In a very basic embodiment each panel shows only one curve, defining a
concave or convex shape of the assembly. Said one curve could be
sinusoidal, elliptical, circular, or any other bow shape.
In a more complex embodiment each panel shows two or more adjacent curves.
These adjacent curves can define a number of adjacent concave (or convex)
surface sections of the assembly. On the other hand the adjacent curves
can also define alternating convex and concave surface sections of the
assembly. In that case the assembly in its unfolded state looks like a
corrugated board.
The curves as such can be made in different ways. Conceivable is that each
curve is obtained as a fluent bend of the panel. Also conceivable is that
each curve is obtained by a discrete number of bends with flat panel
sections in between.
In a preferred embodiment the panels are made of a resilient preformed
material such that in the folded state each panel is stretched to a flat
shape, whereas after unfolding each panel resumes its preformed curved
shape. In that case no separate shaping or tensioning means are necessary
in space to obtain the curved shape of the various panels. However, during
transport from earth into orbit the panels have to be stretched into a
flat shape, which under circumstances could be considered a disadvantage
because, for example, of the stresses on the skins.
In another preferred embodiment the panels are formed as flat panels and
the assembly comprises mechanical means which after unfolding of the
assembly can be activated to obtain the desired curvatures in the panels.
In that case there is no stress in the panels during transport into orbit,
but separate means containing sufficient energy to pre-load the panels are
necessary to obtain the curved shape of the panels.
The above-mentioned mechanical means may consist of tensioning means
connected at least to both side edges (the edges not connected to the
hinges) of a panel being able to draw these to side edges towards each
other over a predetermined distance.
As an example the tensioning means comprise wires and fasteners for
shortening the length of said wires.
As alternative the mechanical means may comprise a number of bow shaped
bridging elements, initially lying flat on the surface of a panel,
connected near the side edges to the respective panel and connected with
its bow shaped side at at least one further place to the surface of said
panel, such that after bringing this bridging element into a state wherein
it projects from the surface the panel is forced to assume its desired
curved shape.
In all embodiments the hinges interconnecting the various panels should
allow the reshaping of the panels. In other words it is preferred that the
hinges are embodied such that the transformation from a flat panel into a
curved panel is not impeded. As an example the hinges could be formed as
stripes of a resilient material. The hinges can also be embodies as
elongated hinges extending along the major part of the edges to be
interconnected and having enough flexibility to enable curving of the
respective panels. As alternative the hinges can be embodied as relatively
small hinges of arbitrary construction, a number of which are, in a bow,
attached to the edges to be interconnected.
The invention will now be explained in more detail with reference to the
attached drawings.
FIG. 1 illustrates three views on a first embodiment of a solar panel
assembly according to the invention. FIG. 1a shows the folded situation
during transport, FIG. 1b the situation during unfolding and FIG. 1c the
ultimate extended position during operation in space.
FIGS. 2a and 2b illustrates a second embodiment of an assembly according to
the invention in which tensioning wires are used to obtain the bended
shape.
FIG. 3 illustrates a third embodiment of an assembly according to the
invention in which a bow shaped bridge is used. FIG. 3a shows the bridge
resting against the surface of the panel and FIG. 3b shows the bridge in
the active outwards projecting state tensioning the panel into a bow
shape.
FIGS. 4a and 4b illustrate two embodiments in which the bow shape is not
obtained by a fluent bend but obtained by a discrete number of relatively
sharper bends with flat panel sections in between.
FIG. 5 illustrates an embodiment wherein the unfolded solar panel assembly
has the appearance of a corrugated board, whereby each panel shows three
alternating curves.
FIG. 6 shows a cross section through one of the panels in FIG. 5.
FIG. 7 shows a cross section through another embodiment wherein each panel
has a number of adjacent concave (or convex) curves.
The FIGS. 1a, 1b and 1c illustrate very schematically a satellite 10
comprising a defoldable solar panel assembly 20. Through a yoke mechanism
30 the solar panel assembly 20 is connected to the actual satellite 10.
In FIG. 1a the situation during transport from the earth to the orbit is
illustrated. The solar panel 20 is folded and located directly adjacent to
the central body of the satellite 10. In this state the whole assembly
occupies only a limited volume and fits in the cargo space of the
transport vehicle (rocket, space shuttle, etc.) such that the available
space is used optimally. The forces of the holddown or the restraint
points ensure that the panels are tightly stowed during launch.
In FIG. 1b the situation is illustrated during the refolding or defolding
operation of the panel assembly. It is assumed that the satellite 10 has
reached its orbit and has received instructions to defold the assembly 20.
In FIG. 1b the separate panels 21, 22, 23, 24, 25 and 26 of the solar
panel assembly are already visible.
In FIG. 1c the ultimate situation is illustrated whereby all panels 21, . .
. , 26 of the solar panel assembly 20 are in one plane. In FIG. 1c
furthermore the hinges between the various panels are indicated with
reference numbers 41, 42, 43, 44 and 45. It is assumed in all FIGS. 2a, 2b
and 2c that the solar cells are installed at the non visible underside and
that the solar radiation impinges on the panel from the direction Z.
As clearly visible in FIG. 1c all panels are slightly bended and because of
that the curved panels have obtained an inherent stiffness. The panels are
made of a material which is sufficiently resilient to bring the whole
assembly into the state illustrated in FIG. 1a. Thereby the panels are
forced into a flat shape. After unfolding the package each panel resumes
its original slightly bended shape.
Preferably, the yoke 30 has three arms 30a, 30b, 30c. The ends of these
arms, which are connected to the first panel 21, are preferably located at
a curved line such that this panel 21 is more or less forced into a curved
state. In this manner even panels which are straight themselves can be
forced into a bended shape.
The detailed construction of the yoke 30 is considered known to the expert
reader and therefore further explanation of its construction and operation
is considered superfluous.
To be able to obtain its curved shape the various hinges 41, . . . , 45
should have sufficient flexibility to allow the assembly as a whole to
obtain its curved shape. That implies that each of the hinges is made of a
construction with inherent flexibility or is made of material which as
such is flexible enough. Various solutions are considered within reach of
the expert reader, so that the provision of further details is considered
superfluous.
FIG. 2a illustrates an embodiment of one panel of an assembly according to
the invention in which tensioning wires are used to obtain the bended
curved shape. One panel 30 is shown which originally is a flat panel. By
means of a wire the panel is bended. The tensioning wire is attached to
the side edge 30a and through a fastener 34 to the side edge 30b (the
edges not occupied by the interconnecting hinges). In the folded state of
the assembly there is no tension on the wire and the panel is flat. After
unfolding the assembly the fastening means 34 receive an instruction to
shorten the length of the wire 32 such that the panel becomes bended and
obtains a predetermined bow shape as illustrated. The fastener means for
operating the wire can have various embodiments and are assumed known to
the solar panel technician so that a further explanation thereof is
superfluous.
Instead of a fastener also a shrinking wire can be used of which the length
will shrink under the influence of for instance an electrical current,
heat, etc.
FIG. 2b illustrates a more preferred embodiment of an assembly according to
the invention in which two crosswise extending tensioning wires 38a and
38b (or shrinking wires) are used to obtain the curved shape. The
tensioning wires are attached to the edges 31a and 31b of the panel 31
whereby fasteners 36a and 36b are installed to tension the wires and bring
the panel from its flat shape into the desired curved shape. The use of
two wires results into additional advantages. Two cross wires provide an
additional stiffness in comparison with the situation with only one
tensioning wire. Furthermore, each wire will backup for the other, in case
one of the wires fails to perform its function then there is still the
other wire.
FIG. 3 illustrates a third embodiment of an assembly according to the
invention in which a bow shaped bridge is used for bending the panel. FIG.
3a shows the bridge 42 resting against the surface of the panel 40. The
bridge 42 is connected by means of flexible or adjustable connections 44a,
44b and 44c to the panel 40 near the side edges 40a and 40b thereof. At
least one further flexible connection 44b is made somewhere in between the
connections 44a and 44c. After unfolding the assembly the bridge 42 is
moved upwards by not illustrated means into an active outwards projecting
state as illustrated in FIG. 3b tensioning the panel 40 into a bow shape.
Instead of a fluent slow bend as in FIGS. 1, 2 and 3 also a discrete number
of relatively sharper bends with flat panel sections in between can lead
to the desired result. Examples thereof, which fall within the scope of
the invention, are illustrated in FIGS. 4a and 4b. FIG. 4a illustrates an
embodiment in which a panel 50 by means of a relatively sharp bend 52 is
divided into two flat sections 50a and 50b. Through this sharp bend 52 the
panel 50 as a whole has obtained a bow shape and falls within the scope of
the invention. The material of the panel should have a certain flexibility
at least around the bend area 52 to enable folding the panels into a
package in which the panels are forced into a substantially flat shape.
FIG. 4b illustrates an embodiment in which a panel 60 by means of two
relatively sharp bends 62 and 64 is divided into three flat sections 60a,
60b and 60c. Through these sharp bends 62 and 64 the panel 60 as a whole
has obtained a bow shape and falls within the scope of the invention. Also
in this embodiment the material of the panel should have a certain
flexibility at least around the bend areas 62 and 64 to enable folding the
panels into a package in which the panels are forced into a substantially
flat shape.
FIG. 5 illustrates an embodiment of an solar panel assembly according to
the invention whereby the assembly has the appearance of a corrugated
board. The assembly is shown in its unfolded state in space and comprises
four panels 71, 72, 73, and 74 which are hingedly attached to each other.
Instead of elongated hinges of a rather flexible material, as is assumed
in the embodiment of FIG. 1c, the various panels 71, . . . , 74 are
interconnected by means of a restricted number of small hinges, in this
case three hinges between each combination of two solar panels. The nine
hinges are indicated by 81, . . . , 89.
To obtain the corrugated shape illustrated in FIG. 5 one could use panels
made of a preformed material. The panels in their untensioned state have
the shown corrugated shape. The panels have to be resilient enough to
enable folding them into a package as illustrated in FIG. 1a whereby each
panel is forced to adopt a straight shape.
However, as illustrated in FIG. 6, also the use of tensioning wires is
conceivable. In FIG. 6 a cross section through one of the panels 74 is
shown. The panel has two small openings 74a and 74b through which a wire
77 extends. One end of the wire is connected to a fastener 76 attached to
one edge of the panel 74 and the other end of the wire 77 is connected at
78 to the other opposed edge of the panel 74. If the wire is tensioned by
means of the fastener 76 then the panel will obtain a curved shape with in
this case three alternating curves.
In FIG. 6 part of the wire 77 extends across the lower surface of the
assembly, i.e. the surface on which the sunlight is impinging. An
alternative embodiment wherein the wire 77' extends solely across the
upper surface of the assembly is illustrated in dashed lines. On the
left-hand side an upstanding fastener 76' is attached to the assembly
whereas at the right-hand side an extending mounting element 78' is
fastened to the assembly. The wire 77' is attached to the element 78' and
to the fastener 76' and runs in the centre of the assembly through a
ring-shaped element 79'.
The embodiment shown in cross section in FIG. 6 has three adjacent curves.
More especially the shown embodiment has alternating convex and concave
curves which fluently pass into each other.
The embodiment illustrated in cross section in FIG. 7 has a number of
adjacent curves, each formed as a concave (or convex) section. The three
sections are indicated by 80, 81, and 82. If this panel is made of a
preformed material then no further measures are necessary for shaping the
panel. However, if the panel is originally flat, then for instance a wire
84 could be used to shape the panel in its desired curved form. At the
right-hand side of the figure the wire 84 is, at 85, connected to one edge
of the panel, whereas at the left-hand side a fastener 86 is used to
connect the wire to the respective edge of the panel. The wire extends
through two ring-shaped elements 87 and 88 fixed to the panel at the
transition of two curves.
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